Renal Transplant Patients Biopsied for Cause and Tested for C4d, DSA, and IgG Subclasses and C1q: Which Humoral Markers Improve Diagnosis and Outcomes?

The association between donor specific antibodies (DSA) and renal transplant rejection has been generally established, but there are cases when a DSA is present without rejection. We examined 73 renal transplant recipients biopsied for transplant dysfunction with DSA test results available: 23 patients diffusely positive for C4d (C4d+), 25 patients focally positive for C4d, and 25 patients negative for C4d (C4d-). We performed C1q and IgG subclass testing in our DSA+ and C4d+ patient group. Graft outcomes were determined for the C4d+ group. All 23 C4d+ patients had IgG DSA with an average of 12,500 MFI (cumulative DSA MFI). The C4d- patients had average DSA less than 500 MFI. Among the patients with C4d+ biopsies, 100% had IgG DSA, 70% had C1q+ DSA, and 83% had complement fixing IgG subclass antibodies. Interestingly, IgG4 was seen in 10 of the 23 recipients' sera, but always along with complement fixing IgG1, and we have previously seen excellent function in patients when IgG4 DSA exists alone. Cumulative DSA above 10,000 MFI were associated with C4d deposition and complement fixation. There was no significant correlation between graft loss and C1q positivity, and IgG subclass analysis seemed to be a better correlate for complement fixing antibodies in the C4d+ patient group.

Reduction of HLA class I expression by ribonucleic acid interference mitigates allogenicity of human primary and Immortalized cells.

Unmatched human leukocyte antigens (HLA) expressed by allogeneic donor cells are the major target for immunological rejection. In order to reduce the immunogenicity of allograft cells, we have developed lentiviral vectors for delivery of short hairpin ribonucleic acid (shRNA) against Class I HLA. This approach was evaluated in both an established human embryonic kidney cell line and primary human CD34+ hematopoietic stem/progenitor cells. Target cells transduced with lentiviral vectors expressing either HLA-A*0201 allele-specific or HLA-A, -B, -C consensus sequence-specific shRNA showed effective knockdown of cell surface HLA expression. Mixed lymphocyte-target cell reactions showed significantly reduced interferon-gamma production from alloreactive cytotoxic T lymphocytes and significantly reduced levels of target cell apoptosis after shRNA-mediated knockdown of HLA expression and target cell survival correlated with vector transduction efficiency. Furthermore, increasing resistance to complement-dependent cytotoxicity mediated by anti-HLA antibodies was observed to correlate with increasing levels of shRNA vector transduction in primary human CD34+ cells. Notably, non-HLA restricted killing by lymphokine-activated killer cells was not incurred after HLA knockdown. These data demonstrate the potential for genetic engineering strategies targeting incompatible HLA alleles to reduce both cellular and humoral responses and enable graft survival after transplantation of allogeneic cells and tissues.

Immunoglobulin G subclass analysis of HLA donor specific antibodies in heart and renal transplant recipients.

Immunoglobulin G (IgG) subclasses IgG1 (G1) and lgG3 (G3) can induce complement dependent cytotoxicity (CDC) and bind to Fc receptors (FcR), which induces phagocytosis and antibody dependent cellular cytotoxicity. In contrast, IgG2 has low CDC activity, lgG4 (G4) has no CDC activity, and neither binds high affinity FcR. Seven transplant recipients were analyzed for G1- G4 human leukocyte antigen (HLA) donor-specific antibodies (DSAs); six had active rejection and one had stable function. Patients with rejection had equal numbers of DSAs, which were G1 and G3, but no G4. The predominant DSAs were directed against HLA Class II proteins. Even with successful anti-rejection therapy, DSA persisted, albeit in several instances with lowered levels. Our findings are consistent with the presence of CDC-inducing G1 and G3 subclass DSAs during rejection. One heart transplant recipient followed for over 42 months had consistent, continuous G4 HLA DSA and stable function. We hypothesize that the presence of G4 DSA in the heart transplant recipient is akin to the allergen specific G4 that has been found in allergic desensitization tolerance, controlled by regulatory T-cells, and that manipulating G4 class switching through HLA antigen desensitzation could produce a tolerant state.

Impact of hepatitis C infection on outcomes after heart transplantation.

BACKGROUND: Prevalence of hepatitis C infection (HCV) among heart transplant (OHT) recipients ranges from 7% to 18%. Despite the paucity of data regarding the outcomes of heart transplant recipients who are HCV positive before transplant, many transplant centers are declining to perform OHT in HCV-seropositive patients. METHODS: We assessed the clinical outcome of HCV-seropositive compared with HCV-seronegative heart transplant recipients using the Organ Procurement and Transplant Network/the United Network for Organ Sharing database. Between January 1, 2000, and December 31, 2005, 224 HCV-seropositive and 10,406 HCV-seronegative recipients who received HCV-seronegative donor organs were identified. RESULTS: Overall patient survival rates of HCV-seropositive recipients were significantly lower than those of HCV-seronegative recipients (84.8% at 1 year, 77.1% 3 years, 68.9% 5 years for HCV-seropositive group vs. 87.9% at 1 year, 80.7% 3 years, and 74.1% 5 years for HCV-negative recipients, log rank P=0.036). However, adjusted relative risk of recipient HCV-seropositive versus HCV-seronegative status did not reach to statistical significance level (relative risk=1.23 with P=0.087) after adjusting for other donor and recipient factors. Causes of death among HCV-seropositive and HCV-seronegative groups were similar. Cumulative incidence of an acute rejection episode in the first year after transplantation among HCV-seropositive recipients was 35.7% versus 32.6% HCV-seronegative recipients (P=0.32). CONCLUSIONS: A more rational approach should be developed for the management of HCV-seropositive heart transplant candidates. Carefully selected HCV-seropositive patients should not be excluded from OHT.

Comparison of renal allograft outcomes in combined liver-kidney transplantation versus subsequent kidney transplantation in liver transplant recipients: Analysis of UNOS Database.

BACKGROUND: There may be an allograft-enhancing effect by the liver on the renal allograft in the setting of simultaneous combined liver-kidney transplantation (CLKT) from the same donor. This study was performed to investigate whether an existing liver allograft could protect a kidney allograft from immunologic injury due to histoincompatibility in liver transplant recipients who received sequential kidney transplantation (KALT). METHODS: Using the United Network for Organ Sharing database covering January 1996 to December 2003, outcomes of 352 KALT were compared to 1,136 CLKT. Incidence of acute and chronic rejection and rejection-free renal graft survival was compared between two groups. RESULTS: Renal half-life of KALT allografts was shorter than CLKT group (6.6+/-0.9 vs. 11.7+/-1.3 years, P < 0.001). Incidence of chronic rejection in KALT group was higher than CLKT group (4.6 vs. 1.2%, P < 0.001). One and three-year rejection-free renal graft survival of KALT and CLKT groups were different (77% and 67% KALT vs. 85% and 78% CLKT, respectively; P < 0.001). Among human leukocyte antigen mismatched and sensitized patients, rejection-free renal graft survival of KALT group was inferior to the CLKT group (75% at 1 year and 61% 3 years vs. 86% at 1 year and 79% 3 years, P < 0.001). CONCLUSION: Liver allograft provided renal graft immunoprotection if both organs are transplanted simultaneously (immunogenetic identity), but not for kidneys transplanted subsequently.